RADIO NOTES

Dominion, Volume 26, Issue 287, 30 August 1933, Page 6

RADIO NOTES

By

"ETHER"

: CURRENT TOPICS Marchese Marconi intends to.start within the next few days, on a new cruise in his steam yacht “Elettra” for the purpose of carrying out further experiments in the transmission and reception of' micro-waves — wireless waves of less than one metre length. In addition to repeating and checking his long distance tests of last year, when micro-wave signals were transmitted and received over the record distance of 168 statute miles, Marchese Marconi has planned a new series of-investiga-tions into the propagation properties of these waves. „ It. is hoped that his investigations . will lead to further- important discoveries opening the way fo the wider application of micro-;waves for wireless telephone and telegraph services. Elaborate preparations for the new cruise have been ■ made for months past at the Marconi Works in Italy, on board the yacht ‘'Elettra,” and at Marchese Marconi’s experimental micro-wave stations at Santa Margherita Llgure and Rocca di Papa, near Rome, . . '■■■•' ’ - . * The' ithrned Judge at Bow County Court is evidently one who moves with the times.' 'ln trying a wireless hire-purchase-case which came before himrecently, he said: ‘‘lf a three-valve radio set will not get more than the London Regional and National stations, it was not worth £35 when it was bought, or now.” The “owner” of the set explained that on Sundays he wanted a change from church niusie, but foreign stations completely eluded him. When he had said “Regional’ and "National” he had said all. And the judge ruled that he’ could send the set back to the firm which supplied it. ♦ ♦ *. At a York conference of rural listeners, convened by the 8.8.C.’s Central Council of the Adult Education Section, a Beverley gentleman, with that, charming bluntness which is characteristic of Yorksliiremen, complained that rural listeners could not understand the experts when they spoke on agricultural economics. Unwanted a practical farmer,- not an “expert.” * »■' ■ Owing to the economic crisis, a number of French firms which had signed publicity contracts with -broadcasting stations have been unable to. pay the piper-after the programmes'have been broadcast. The stations have had no alternative but to accept payment in kind, with the result that the managerial offices of some; studios are now replete with magnificent-carpets, tablecloths) and other trimmings. One station received a letter from a defaulter in thes? terms: “The state of my treasury compels pre to, ask you to accept 200 Yo-Yos and a number of dolls, each of which says ‘Mamma’ simply on being squeezed." • ’.. [ \' ' ' : .The engineering work of the 8.8. C. has; never failed to maintain a very high standard of excellence, and is one of the aspects of the Corporation which has never caused adverse criticism. During 1932 there were 58,163 hours of transmission for all stations, and the average, breakdown time was only 0.023 per cent., as against 0.03 per cent, for 1031. Considering" the kind of .plant used by .broadcasting stations—more complicated than that of electrical power stations, for example, this showing is highly creditable. In connection with broadcasting, a listener in the Hutt area ■says that results in the evenings may ■not be good. Morning reception, however, is excellent. The Empire, authorities have 1 recently instituted a special ■broadcast from 7,30 a.m. to 10 a.m. for New Zealand. This transmission is on 25 metres and arrives from England along the western route. A specialdirectional aerial is used. The suggestion that now and again the radio authorities might make use of this is a sound one. Indeed as things stand at present it is better, to receive the Empire station at breakfast than not at all. ’ 7

DOOR BAFFLES Although the idea is not. a new one, ic may be pointed out that a communicating door between two rooms makes one 'of the most satisfactory baffles that can be contrived for • a .movingcoir loudspeaker of the cone type;. On aesthetic -grounds the use of a; door for this purpose may not suit everyone, but with a little forethought and ingenuity it is often possible to mount the loudspeaker so that it; is not unsightly; at any rate, the front of the .aperture behind which the cone is mounted may be camouflaged quite successfully. ‘The hole may be covered with metal gauze, held in position by a circular beading, the whole being painted in the same colour as the door. • ; ■ With regard to the back of the door. , it will, generally be necessary to boxin the loudspeaker. The back of the box. again, may be covered in with fabric or gauze, but should not 'be filled in with solid, material. If the door is lightly built, resonances may be largely avoided by mounting the loudspeaker on a heavy backing board before securing it in position. “SPAGHETTI” REPAIRS Spaghetti resistances, through illhandling, sometimes develop a break in tlie winding. Provided the damage is small a repair can be affected in the following manner;—. \ First remove one end connector, then gently slide off the systoflex covering, locate the break by using a couple of pins as test-prods in series with ’phones and dry cell. Clean the wire round the break by lightly dabbing it with line emery paper. Then wrap a piece of tinfoil round this cleaned portion, tie with cotton and replace the systoflex and connector. The resistance is naturally reduced a little and care must be taken that the current is well within the former rating of the resistor, t . <- FORMULA FOR MORTAR “Amateur” asks for a formula for mortar to be used in the construction of a brick wall against which he intends building a small rockery. The wall will be about 3ft. high and in single bride. For every 6ft. of walling build a brick pier (9in. x 4|in.). The mortar should be composed of four parts of sand to one part of cement.' In order to give the wall additional strength, lay two strands of No. 8 galvanised fencing wire in the mortar about halfway up the wall. Again, cut in short lengths ahey can be used for mounting components raised from the baseboard.

INTERFERENCE Suppressor Suggestions THRESHOLD CONTROL i There are, of course, different types of interference, and some noises are more difficult to deal with than others. The interference due to switching on and off electric lights on the same circuit (in the case of a mains receiver), and the noises du.e to flashing signs, ? electric motors, and so on, are difficult to cut out. ' But the general background of static, which you get on long-dis-tance reception, can now be largely got over by the use of various types of noise suppressor. The action of these dodges is rather like that of the'driver of a car who drives in such a way as to avoid as far as possible bumps and bad places in the road. The manufacturer.of the car does as much as he can in the way of design, .springs, and so on, to smooth out the bumps of the road, but even when he has done his best a certain amount still remains with the driver of the car; two different drivers will get quite different performances out of the same ear. . Bv means of the suppressor you can adjust until the background noise becomes practically inaudible, the adjustment being made while the receiver Is detuned and set to maximum volume. Having made this adjustment you can then tune the set to different points on the dial or adjust the volume to any desired level within limits without being seriously bothered with the noise. Only signals which have a sufficient Intensity to stand out from the background noise will get through to any appreciable extent. \ The set manufacturer makes the set ; as sensitive as possible so as to give it good all-round characteristics and dis-tance-getting qualities This high sensitivity, however, by the same token, mak.es the set sensitive to noise disturbances, and you can' only, expect good reception when there Is a pronounced difference between the loudness of the desired signal and the loudness of the background noise. The suppression control adjusts the sensitivity of the receiver so that It cannot appreciably respond to the prevailing noise, but hears signals which rise prominently above the background. The noise level will vary for different places and from time to time, so that the maker of the set has to leave the suppression control adjustable in order to allow the user to adapt it to varying conditions.

“SQUEAK-BOXES” Next Year's Reviews? THE MIDGET COMPLEX With the Olympia Exhibition not much more than a month ahead of them, most manufacturers will already have decided on all the main details of their programme for next season, says the “Wirelss World.”- Valves.have now an all-important-influence on receiver design, and, if only for the reason that so many multi-electrode types have recently Ibeen Introduced, we are bound to have.an exhibition that will be full of technical interest. '../<• Is the “midget” set, with a frontal area of about six inches and a.depth no greater than that of a fair-sized book, to figure prominently on the programme? In spite of suggestions that this phase of developmentmight well be short-circuited, many British manufacturers, influenced by the undoubted commercial success of this type of set in America, have gone to the length of developing experimental models. Whether many ■ of these “squeakboxes,” as they are now contemptuously called, in the land of their origin, wllf finally get on the market is uncertain; if they are offered to the public purely as auxiliary sets, there will be little* cause for complaint, but unless some genius manages to obtain better quality than that of the average specimen, the pfestige of broadcast, reproduction is bound to suffer in the long run. ‘ ■' There can, of course, be no valid objection to a set merely because it is small; on the contrary, compactness is obviously to be wished for. Uneasiness on this subject is felt only because hitherto it has been found impossible to combine extreme compactness and quality. The permissible size of the loudspeaker and. its baffle area is too small, and is, indeed,, the main’limiting factor. .. ■ . ‘ . This naturally suggests the possibility of developing a real midget set — smaller even than existing types—to work with an external loudspeaker. Such a plan overcomes all the more serious objections, and has its own special advantages.. It is interesting to hear that at least one firm expects to produce a set on these lines. . EMPIRE PROGRAMMES There is renewed agitation about the quality of the programmes: the 8.8.C.' is providing for the Empire through its short-wave service. Some time ago complaints on this subject were met by the 8.8. C. with the argument that, after all, they had to do all the paying, and therefore overseas, listeners had no right to criticise,; To this retort people overseas have replied that the 8.8. C., after waiting in'vain for two years for co-operative financing, suddenly reversed their policy and made a great show of. their ability to provide a service which would be so acceptable to the Dominions and colonies that there would be no question of co-operation in finance. Now listeners overseas are suggesting that the 8.8. C. cannot have it both ways. If the policy is to provide a service so attractive as to enlist support, then bv all means try it out; but it is a corollary to this policy that the 8.8. C. pay special attention to the criticisms and suggestions of its overseas listeners. SHORT-WAVE CHOKE Quite an efficient short-wave/choke can be made on a 1 or lj-in. diameter former of glass or ebonite. ■' One of the small chemical test tubes is quite satisfactory. s ”. About 100 turns of 34 or 36 S.S.C. wire should be wound on the -choke former, a space equal to the thickness of the wire being left -between turnsThe former will need to be about 2j in. long. ; A hollow glass, former can be fixed on the baseboard by screwing down a cork which just fits the glass. The end turns may be fixed by a touch of Chatterton’s compound or glue. Another -way Is to bind a strip of sticky insulation tape at each end.